Sheet removing apparatus

ABSTRACT

Apparatus is provided for separating a copy sheet bearing an unfused toner image from a moving electrophotographic surface to which the copy sheet is electrostatically attracted during the image transfer operation. The separating apparatus utilizes a nozzle assembly having a plurality of nozzles mounted near the electrophotographic surface. A high velocity flow of pressurized fluid from the nozzles for a predetermined time is sufficient to detact the leading edge of the sheet and a lower velocity flow of pressurized fluid from the nozzles is sufficient to hold the copy sheet closely adjacent to the nozzle assembly and permit movement of the copy sheet across the nozzle assembly to a sheet transport toward a fusing station.

United States Patent Crawford Jan. 8, 1974 SHEET REMOVING APPARATUSPrimary Examiner-Richard E. Aegerter [75] Inventor: Roy P. Crawford,Saratoga, Calif. Attorney-Otto Schmld et [73] Assignee: InternationalBusiness Machines Corporation, Armonk, N.Y. [57] ABSTRACT [22] Filed Dec27 1971 Apparatus is provided for separating a copy sheet bearing anunfused toner image from a moving elec- [21] App]. No.: 212,359trophotographic surface to which the copy sheet is electrostaticallyattracted during the image transfer [52] U S Cl 271/80 271/51 operation.The separating apparatus utilizes a nozzle [51] B65h 5/06 assemblyhaving a plurality of nozzles mounted near [58] Fie'ld DIG 2 theelectrophotographic surface. A high velocity flow 271/74 3 2 ofpressurized fluid from the nozzles for a predetermined time issufficient to detact the leading edge of the sheet and a lower velocityflow of pressurized fluid [56] References Cited from the nozzles issufficient to hold the copy sheet UNITED STATES PATENTS closely adjacentto the nozzle assembly and permit 3,506,259 4/l970 Caldwell 271/80movement of the copy sheet across the nozzle assemgq t bly to a sheettransport toward a fusing station. U mgs v CONTROL MEANS 9 Claims, 8Drawing Figures PAIENIEDJAN 3.784.190

SHLU 1 0F 3 PAIENTEDJm SL974 SHEU 2 [IF 3 M FIG. 4

Pmmuum 81914 SHEET 3 HF I! SHEET REMOVING APPARATUS BACKGROUND OF THEINVENTION This invention relates to transfer of anelectrophotographically developed image from an image-bearing member toa suitable transfer sheet and more particularly to apparatus forremoving the transfer sheet from the image-bearing member.

DESCRIPTION OF THE PRIOR ART One prior art apparatus for transferring adeveloped image to a copy sheet comprises a system wherein a coronadischarge device is utilized to produce a charge on the back of the copysheet to attract the image toner from the image-forming surface to thesheet. Due to the transfer charge, an electrostatic bond is producedbetween the image-forming surface and the sheet and this force must beovercome to separate the sheet bearing the toner image from theimage-forming surface.

Mechanical devices such as gripper fingers, air puffers and combinationsof these devices have been used in the past to effect separation. Insome cases an electrostatic charge is produced to neutralize theelectrostatic force which holds the copy sheet to the imageformingsurface so that the copy sheet can be more easily separated from theimage-forming surface.

These prior art systems have been effective to varying degrees in thepast; however, as processing speeds have increased, these prior artmethods are no longer effective to reliably separate the copy sheetsfrom the image-forming surface without damaging the unfused images whichare loosely adhered to the copy sheet.

It is therefore, a primary object of this invention to provide improvedapparatus for separating an imagebearing copy sheet from animage-forming surface.

It is another object of this invention to provide apparatus forseparating an image-bearing copy sheet from an image-forming surfacewithout disturbing the image.

It is a further object of this invention to provide apparatus forreliably separating at high processing speed a copy sheet bearing anunfused toner image from an image-forming surface to which the copysheet is electrostatically attracted.

SUMMARY OF THE INVENTION Briefly, according to the invention, there isprovided apparatus for separating a transfer sheet bearing looselyadhered image forming material from a moving image forming member towhich the transfer sheet is electrostatically attracted comprisingnozzle means mounted adjacent the image forming member for producing ahigh velocity flow of pressurized fluid from the nozzle means for apredetermined time for detaching the leading edge of the transfer sheetand for then producing a low velocity flow of pressurized fluid from thenozzle means to move the transfer sheet adjacent to the nozzle means topermit movement of the transfer sheet across the nozzle means to autilization station.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic schematicview of electrophotographic imaging apparatus embodying the sheetremoving apparatus of the present invention;

FIG. 2 is a partial side elevation of the sheet removing apparatus shownin FIG. 1;

FIG. 3 is a section view along the lines 33 of the nozzle assembly shownin FIG. 6;

FIG. 4 is a section view of an alternate embodiment of the nozzleassembly embodying the invention;

FIG. 5 is a plot of pressure applied to the nozzle assembly on a timescale;

FIG. 6 is a schematic diagram of the air control system for the nozzleassembly;

FIG. 7 is a plot of the control signals on a time basis applied toselectively control the sheet removing apparatus of the invention;

FIG. 8 is a section view of a further embodiment of the nozzle assemblyaccording to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS An example of a particularapparatus in which the subject invention is adapted for use is theelectrophotographic imaging apparatus shown in FIG. 1. In this apparatusa rotatable drum 10 carries around its periphery an electrophotographicphotoconductive member 12 on which is directed an image which is desiredto be reproduced on a suitable insulating transfer member such as copysheet 14. Drum 10 is driven by suitable belts or gears (not shown) frommotor 11 and electrical signals to provide the required control andsynchronization of the machine components are provided by control means15 which may be a computer of an associated data processing system ifdesired. The surface of the photoconductor 12 is uniformly charged to apredetermined polarity by corona discharge device 16. The image to bereproduced is provided in a form so that a suitable exposure means isoperable to direct the image to exposure station 18 onto the surface ofthe photoconductor 12. Relative motion may be provided during exposureof the image at a speed synchronized with the surface speed of drum 10in a manner known in the art. Where the photoconductive surface isilluminated by the image, the surface is discharged leaving a chargepattern in the form of the image to be copied. Either the desired imageor the background area may be discharged to produce the desired chargepattern, depending upon whether direct or reversal development is to beused.

Thereafter the drum passes a development station 20 at which a tonercarrier mixture 22 is cascaded across i or otherwise brought in contactwith the electrostatic image on the surface of the photoconductor 12 asis known in the art. The toner having a charge opposite from thepolarity of the electrostatic image charge is attracted to the drumsurface to render the image visible.

Continuing the clockwise rotation of the drum 10, a copy sheet 14 is fedinto contact with the developed eleectrostatic image by the transportmeans 24. A corona discharge device 26 is disposed above the copy sheetat the area of contact with the drum. Corona discharge device 26produces ionization of a polarity opposite that of the toner sufficientto attract the toner forming the image to the copy sheet. After thistransfer operation, the copy sheet 14 is separated from the drum byseparator means 30 and fed by transport means 38 past a fusing station40 which serves to fuse and permanently fix the image-forming toner tothe copy sheet. The nature of the separating means 30 will be describedin more detail later. Since transfer of all the image toner 27 is notusually accomplished, residual toner 28 remains on the drum surfaceafter a transfer operation. The drum continues to rotate past a cleaningapparatus 32 which cleans the surface of the photoconductor and removesany excess toner. If desired, a pre-clean-corona 29 and an erase lamp 3]may bev placed before cleaning station 32' to aid in cleaning I thephotoconductor. This'op'eration completes the cycling of the drum forreproducing the desired image.

A sheet separating operation is initiated by a signal FEED SHEET whichis generated by control means 15. The signal is generated in synchronismwith the position of the image on drum so that a sheet 14 is fed tomerge with the toned image on drum 10. The FEED SHEET signal is coupledto actuate single revolution clutch 76 for one cycle of operation of thefeed components connected by dashed lines. A cycle of operation resultsin a sheet being fed from the position shown in FIG. 2 to the drum toreceive the toned image from drum 10 while a second sheet is being fedfrom hopper 78 to be registered at stop 80. The motion of pressure roll82 to an operative position is coordinated with the position of stop 80so that stop 80 is moved out of the path of the sheet before thepressure roll 82 is lowered to drive sheet 14. Stop 80 is then moved tothe operative position prior to the arrival of the second sheet so thatthe second sheet is properly registered at stop 80.

Sheet 14 is fed to coincide with the toned image on the drum. Thetransfer corona is energized to produce ions of the proper polaritywhich are sprayed on the back of sheet 14 to electrostatically attractthe image toner to sheet 14. Sheet 14 with the toned image looselyadhering to the surface is then separated from drum 10 by separatormeans 30.

Separator means 30 comprises a nozzle assembly 34 which is mounted in afixed position near the surface of drum 10. Nozzle assembly 34 comprisesa plurality of individual nozzles 36 through each of which a relativelyhigh velocity stream of pressurized fluid is 7 the invention is operableto remove thecopy sheet ejected as the leading edge of copy sheet 14approaches the nozzle assembly. The individual nozzles are designed toproduce a blast of fluid directed substantially tangentially to thesurface of the drum. Due to copy sheet 14 being wrapped around curveddrum 10, a small portion of the leading edge of the paper may not followthe contour of the drum, thereby making easier the sheet separationoperation. However, even if the leading edge of the sheet is completelytacked down by electrostatic attraction, my invention reliably separatesthe sheet from the drum without damage to the toner image. The blast offluid raises the leading edge of the sheet as the leading edgeapproaches the nozzle 7 exit point. When the leading edge of the sheetis positioned approximately opposite the nozzle exit, a relatively lowervolume of fluid is introduced through the individual nozzles so that themovement of the fluid between the individual nozzles 36 and copy sheet'14 creates a partial vacuum, thereby pulling (by Bernoullis principle)the copy sheet leading edge to a position closely approaching, but nottouching the nozzle assembly. The electrostatic attachment of copy sheet14 to drum l0 continues to drive the leading edge of copy sheet 14 andthe low volume of fluid is effective to guide the sheet in asubstantially friction-free manner to sheet transport means 38. Sheettransport means 38 comprises a suitable transport such as a vacuum belttransport or electrostatic belt transport, which is effective to conveycopy sheet 14 by contacting only the non-image side of sheet 14 througha suitable fusing station 40 in an output means such as stacker 42.

from the image-forming drum at high. speedawith little chance ofdamaging'the unfused toner image; since the.

separator means is in position to blowfluid on the image side of thesheetonly during the passage of the first fraction of an inch of theleading edge of the sheet. Once this fraction of an inch of the leadingedge passes the nozzle 36, the sheet itself is effective to prevent theflow of fluid from reaching the image side of the sheet and all furtherprocessing of the sheet prior to the fusing of the image is accomplishedentirely by contacting the non-image side of copy sheet 14.

One embodiment of nozzle assembly 34 is shown in greater detail in FIGS.2 and 3. The nozzle assembly extends across the surface of drum l0 andis mounted by suitable support means 46 in a fixed position with surface35 spaced a relatively small distance from the drum surface. Anenclosure which extends across assembly 34 is provided to form amanifold 43 in the nozzle assembly for introducing pressurized fluidsuch as compressed air into each of the nozzles 36. A plurality ofindividual nozzles 36 are formed by a contoured opening 45 in themanifold and a shaped diffuser member 44. The nozzle opening 47 formedby fixedly mounting a diffuser member 44 in each contoured opening 45 ispreferably designed to form an annular converging nozzle since thisdesign produces greater efficiencyfor reliably removing a sheet bearingan unfused toner image from drum 10. The number of individual nozzlesused to cover the drum width is a matter of design choice which dependson the air pressure utilized, the rotational speed of the drum, theweight of the paper and the design characteristics of the nozzles.

The pressurized air or other suitable fluid may be provided from anysuitable source which produces a sufficient quantity and pressure of airto overcome the force produced by the electrostatic bond between theimage forming surface and the copy sheet. One embodiment for producingthe desired pressure is shown in FIG. 6. A suitable pump 48 is providedto compress the air for storage in storage tank 50 to which a suitablerelief valve 52 is attached to provide a predetermined maximum pressure.A first solenoid valve 54 is placed in an output line from tank 50 toprovide the pressure to input line 56 for separating the leading edge ofcopy sheet 14 from the image-forming surface when valve 54 is energizedwith a suitable electrical signal generated by control means 15 such asthe PRIMARY NOZZLES signal shown in FIG. 7. A second air path from tank50 is provided with a pressure regulator 58 and a second solenoid valve60 to produce the lower level of pressure suitable for holding the copysheet to the nozzle assembly. Pressure regulator 58 is set so that therequired pressure is provided to input line 62 of nozzle assembly 34when valve 60 is selectively actuated by a suitable electrical signalgenerated by control means 15 such as the signal SECONDARY NOZZLES shownin FIG. 7.

Each of the solenoid valves 54, 60 may be selectively actuated toprovide the pressure to the manifold of nozzle assembly 34. For example,the valves may be actuated at times shown in FIG. 7 to produce the gaspressure as shown in FIG. 5. At time T the sheet is in the approximateposition shown in FIG. 1 approaching the nozzle assembly and valve 54 isenergized to direct the high pressure gas to the nozzle assembly. Attime T, the sheet is located at the approximate position shown in FIG. 4and the lower pressure air is directed to the nozzle assembly by turningoff valve 54 and turning on valve 60. This level of pressure ismaintained until time T when the sheet is at the approximate positionshown in FIG. 3. In some cases the lower pressure gas may be left on atall times and obtain reliable operation in which case valve 60 would notbe necessary.

In some cases the valves 54, 60 may be actuated mechanically by means ofsuitable cams which are timed to coincide with the position of theleading edge of the sheet 14 on drum member 10. However, the position ofthe sheet on the drum may not be located accurately enough for reliableoperation of the separating apparatus, particularly in machines whichoperate at high process speeds. In other machines the sheet isaccurately located on the drum but at a random position on the drum. Itis, therefore, preferable to have valves that are selectively operableaccording to an electric signal which is generated in synchronism withthe position of the sheet on the drum. In these cases sufficientlyaccurate signals PRIMARY NOZZLES and SECONDARY NOZZLES are generatedfrom the logic control circuits 15 in the machine to actuate the valves54, 60 by applying the signal to lines 55, 61 respectively at-the propertime in the machine cycle to produce reliable separation of the copysheet without damage to the image on the sheet.

In some cases such as very high speed or synchronous machine operation,it may be necessary to provide apparatus for sensing the position of theleading edge of a copy sheet so that a sufficiently accurate signal canbe generated for actuation of valves 54, 60 to separate the sheetwithout damaging the toner image on the sheet. One suitable apparatus(not shown) for sensing the position of the leading edge of a sheetcomprises a light source mounted to produce a beam of light whichimpinges on the surface of drum 10. A suitable sensing apparatus such asa photocell is positioned near the surface of the drum at the point ofimpingement of the light beam on the surface of the drum. Duringoperation when no sheet is present, the surface of drum l0 reflects thelight so that substantially no light reaches the photocell; however,when a sheet is present the light is diffused so that sufficient lightreaches the photocell to produce a detectable signal from the photocelloutput. This signal indicates that the leading edge of a sheet ispresent and the signal is sent to control means 15 and utilized togenerate the signal PRIMARY NOZ- ZLES to actuate the solenoid valve 54for a sufficient time to separate the leading edge of the sheet. Upontermination of the signal PRIMARY NOZZLES for the separating pressure, asecond signal SECONDARY NOZZLES is generated which actuates solenoidvalve 60 to produce the holding level of air for a time sufficient forthe leading edge of sheet 14 to reach sheet transport 38. Thus, it canbe seen that the sheet is under positive control at all times from theseparation of the sheet until the image is fused to copy sheet 14.

For higher process speeds the alternate embodiment of nozzle assembly 34shown in FIG. 4 may produce more reliable operation. This nozzleassembly utilizes the same primary nozzle assembly that has beenpreviously described; however, an auxiliary nozzle 64 is provided to,ensure even more positive control over the leading edge of the sheet asthe leading edge is guided from the drum to the sheet transport 38 toeliminate any possibility that the sheet may be reattached to thesurface of drum 10. The auxiliary nozzle comprises a manifold enclosureto which pressurized gas is introduced through line 62'. A contouredportion 68 of the valve assembly in conjunction with shaped deflectormember 66 forms the auxiliary nozzle 64 which may extend the width ofsheet 14. Auxiliary nozzle 64 produces a flow of air parallel to thesheet path at the same pressure level as the conveying pressure (such as2 to 4 PSI, for example) in the main nozzle of the embodiment shown inFIG. 3 so that the flow is operable to hold the sheet closely adjacentto the surface but not touching the deflector member 66 of secondarynozzle 64. Since this flow produces no vertical component of force,there is no tendency to force the leading edge of the sheet to reattachitself to the surface of drum 10. This construction has the addedadvantage that the surface of the main nozzle and the surface of theauxiliary nozzle need not be in the same plane, so the auxiliary nozzlemay be utilized to change the angle of the paper path to an extent aswell as providing an added safety factor insofar as prevention ofreattachment of the copy sheet to the surface of the drum 10.

A further embodiment of a nozzle assembly is shown in FIG. 8. The nozzleassembly comprises a first nozzle 72 to which the stripping pressure(such as 6 to 10 PSI, for example) of pressurized gas is applied throughinput 56". Nozzle 72 is followed along the direction of paper travel bya plurality of secondary nozzles 74 to which is applied the conveyinglevel of pressurized gas through input 62". A row of nozzles 72, 74 areprovided across the width of sheet 14 and the position of nozzles may bestaggered if desired.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in the form and detailsmay be made therein without departing from the spirit and scope of theinvention. What is claimed is: 1. Apparatus for'separating a transfersheet having image forming toner particles loosely adhered to onesurface thereof from a moving image forming member to which the transfersheet is electrostatically attracted comprising:

a first transport means to convey the transfer sheet to a transfer area;

nozzle assembly means mounted adjacent the path of travel of thenon-image surface of the transfer sheet, said nozzle assembly meansproducing a first direction of flow of pressurized fluid against thedirection of movement of the transfer sheet and a second direction offlow of pressurized fluid in the direction of movement of the transfersheet;

means for producing a high velocity flow of pressurized fluid from saidnozzle assembly means as each sheet approaches for a predetermined timeto de tach the leading edge of the transfer sheet from the firsttransport means;

second transport means operative on the non-image surface of thetransfer sheet to convey the transfer sheet away from the transfer area;and

means for producing a relatively low velocity flow of pressurized fluidfrom said nozzle assembly means to hold the non-image surface of thetransfer sheet closely adjacent to said nozzle assembly means to guidethe sheet away from the transfer area.

T 23 6 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,784,190 Dated January 8, I974 Inventor(s) y Crawford It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In C01 5, line 28, the word "synchronous" shou1d be "asynchronous".

Signed andsefa led this 11 m of June 1971;. I

- (SEAL) Attest:

EDWARD M.ELET0HER,,JR. c. MARSHALL DANN Attesting Officer Commissionerof Patents

1. Apparatus for separating a transfer sheet having image forming tonerparticles loosely adhered to one surface thereof from a moving imageforming member to which the transfer sheet is electrostaticallyattracted comprising: a first transport means to convey the transfersheet to a transfer area; nozzle assembly means mounted adjacent thepath of travel of the non-image surface of the transfer sheet, saidnozzle assembly means producing a first direction of flow of pressurizedfluid against the direction of movement of the transfer sheet and asecond direction of flow of pressurized fluid in the direction ofmovement of the transfer sheet; means for producing a high velocity flowof pressurized fluid from said nozzle assembly means as each sheetapproaches for a predetermined time to detach the leading edge of thetransfer sheet from the first transport means; second transport meansoperative on the non-image surface of the transfer sheet to convey thetransfer sheet away from the transfer area; and means for producing arelatively low velocity flow of pressurized fluid from said nozzleassembly means to hold the non-image surface of the transfer sheetclosely adjacent to said nozzle assembly means to guide the sheet awayfrom the transfer area.
 2. The invention according to claim 1 whereinsaid nozzle assembly means comprises a plurality of annular convergingnozzles spaced across the transfer sheet.
 3. The invention according toclaim 1 wherein said nozzle assembly means comprises a plurality of rowsof individual nozzles spaced across the transfer sheet.
 4. The inventionaccording to claim 1 wherein said nozzle assembly means comprises afirst and second nozzle means spaced in the direction of movement of thetransfer sheet.
 5. Apparatus for separating a transfer sheet havingimage-forming toner particles loosely adhered to one surface thereoffrom a moving image-forming member to which the transfer sheet iselectrostatically attracted comprising: a first transport means toconvey the transfer sheet to a transfer area; nozzle assembly meansmounted adjacent the path of travel of the non-image surface of thetransfer sheet, said nozzle assembly means producing a first directionof flow of pressurized fluid against the direction of movement of thetransfer sheet and a second direction of flow of pressurized fluid inthe direction of movement of the transfer sheet; means for coupling asource of high pressure fluid to said nozzle assembly means for a firsttime period to detach the leading edge of the sheet from the firsttransport means; second transport means operative on the non-imagesurface of the transfer sheet to convey the sheet away from the transferarea; and means for coupling a relatively low pressure fluid to saidnozzle assembly means for a second time period to hold the non-imagesurface of the sheet closely adjacent to the nozzle assembly means toguide the sheet from the transfer area to the second transport meanswithout disturbing the image-forming toner particles on the imagesurface of the sheet.
 6. The invention according to claim 5 wherein saidnozzle assembly means comprises a first nozzle means for producing saidfirst direction of flow and a second nozzle means for producing saidsecond direction of flow.
 7. The invention according to claim 5 whereinsaid nozzle assembly means comprises a plurality of annular convergingnozzles spaced across the transfer sheeT.
 8. The invention according toclaim 5 wherein said nozzle assembly means comprises a plurality of rowsof individual nozzles spaced across the transver sheet.
 9. The inventionaccording to claim 5 wherein said high pressure fluid source is coupledto said first nozzle means to detach the leading edge of the sheet andsaid relatively low pressure fluid is coupled to said second nozzlemeans to guide the sheet to the second transport means.